In a typical communications network, it is common practice to implement a network topology discovery protocol, which enables a node of the network to populate a respective topology database that may subsequently be used to compute routes through the network. One such network discovery protocol is Open Shortest Path First (OSPF), although there are others.
As is typical of network discovery protocols, OSPF defines various types of Link State Advertisement (LSA) messages, which may be flooded into the network by a node to convey network topology information to all of the other nodes in the network. Accordingly, a given node can use the information contained in received LSAs to populate and maintain its topology database.
In a full-mesh network, both the volume of LSA traffic and the size of the topology database increases with N2, where N is the number of nodes. In a network domain in which there are a large number of nodes, LSA traffic may proliferate and require a very large topology database, both of which may degrade the topology discovery, route computation, and failure recovery functions of the network.
One method of mitigating this problem is to divide a network domain into two or more smaller sub-domains, which may then be connected via one or more designated gateway nodes. The gateway nodes may then implement a Border Gateway Protocol (BGP) to enable computation of routes that originate in one sub-domain and terminate in another. However, in some case this solution is undesirable. For example, a network operator may find the implementation and maintenance of BGP to be onerous or costly.
Another method would be to use External Network to Network Interfaces (E-NNIs) to interconnect sub-domains of a network domain, and utilize sub-domain abstractions to control the topology database sizes and proliferation of related LSAs. However, a network operator again may find the implementation and maintenance of E-NNIs and sub-domain abstractions to be onerous or costly.
Techniques that enable the LSA traffic volume and the size of the topology database to be constrained, while still enabling effective route computation through a network domain, remain highly desirable.